Unpack a coaching logistics board into calendar-ready rows
unpack_coach_logistics_board.RdTransforms a raw coaching logistics board, as returned by
get_monday_board() and augmented with monday_id, site, and L&R name
columns, into a flat tibble of session rows. Unlike PL boards, coaching
boards carry a plain Date of Session column (renamed to Session Date)
rather than a Monday timeline range. List columns are unnested to scalars.